A recent advance in the digital technology has made popular large-capacity discs, such as a DVD and a HDD (hard disk drive), with video data and audio data compressed and recorded on those disk media. In general, data is recorded on a HDD, a DVD-RAM, and a DVD-RW in the DVD-VR standard format. Data is recorded on a DVD-R and a DVD-RW in the DVD-Video standard format with emphasis on the compatibility with the conventional DVD players.
To dub data from disk to disk in a recorder containing different disc drives at the same time, it is required to speedily perform format conversion between DVD formats.
FIG. 1 is a diagram showing the configuration of a DVD-Video format stream (stream 100, cell 101, video object unit (called “VOBU”) 102) and a DVD-VR stream 103.
As shown in the stream 100 in FIG. 1, a DVD-Video format stream includes a plurality of cells each including a plurality of VOBUs.
The VOBU 102 comprises one navigation pack (called “NV_PCK”) provided at the start and containing playback control information; video packs (called “V_PCK”) in which video elementary data is stored and audio packs (called “A_PCK”) in which audio elementary data is stored.
In a DVD-Video format stream, the time information in the stream is reset for each cell. That is, the system clock reference (called “SCR”) is reset to zero on a cell boundary.
Next, the DVD-VR format stream will be described. As shown in the DVD-VR stream 103 in FIG. 1, the DVD-VR stream comprises a plurality of VOBUs. There is one real-time data information pack (called “RDI_PCK”) and a plurality of V_PCKs and A_PCKs.
The DVD-VR format stream has no cell, and the time information is not reset in one stream. Because the DVD-VR format stream has no cell, the SCR value increases monotonously.
In both the DVD-Video format and the DVD-VR format, each of a V_PCK and an A_PCK includes two types of timestamp: one is a presentation timestamp (“V_PTS” and “A_PTS” respectively) that is a playback time for playing back video frames and audio frames included in the pack, and the other is a decoding timestamp (“V_DTS” and “A_DTS” respectively) for decoding video frames and audio frames (PTS and DTS are defined by the MPEG standard for playing back video data and audio data synchronously).
Next, the following describes an example of the method for converting a DVD-Video format stream to a DVD-VR format stream (see Patent Document 1 shown below). Patent Document 1 discloses a conversion device that converts a playback-only DVD format (DVD-R) bit stream to a recording DVD format (DVD-RAM) bit stream. FIG. 12 is a diagram showing a conventional method for converting a DVD-Video format stream to a DVD-VR format stream. FIG. 12 is a schematic diagram for describing the conversion technology, described in Patent Document 1, in an easy-to-understand way. In FIG. 12, NV, V, and A in the DVD-Video format stream represent an NV_PCK, a V_PCK, and an A_PCK, respectively. In the elementary data shown in FIG. 12, I represents an I picture (intra-frame coded screen) defined by the MPEG standard, P represents a P picture (inter-frame coded screen), and B represents a B picture (inter-frame coded screen configured using bi-directional predictions from preceding and following I or P pictures), respectively. An AAU is an MPEG audio access unit. In FIG. 12, RD, V, and A in the converted DVD-VR format stream represent an RDI_PCK, a V_PVK, and an A_PCK, respectively.
As shown in FIG. 12, the video elementary data and the audio elementary data in a V_PCK and an A_PCK in the DVD-Video format stream are analyzed to obtain information on the picture structure of the video elementary data and the number of access units of the audio elementary data (see the picture structure analysis and the audio analysis in FIG. 12). From this information, the information to be used in the DVD-VR format stream is calculated, including the system clock reference SCR used as the time information, the presentation timestamp PTS used as the playback time, and the decoding timestamp DTS used as the decoding time. Based on the calculated time information (SCR, PTS, and DTS), the elementary data is extracted from the DVD-Video format stream and the extracted data is re-multiplexed into a DVD-VR format stream.
[Patent Publication 1]
Japanese Patent Kokai Publication No. JP-P2003-85877A (FIG. 1)
An I picture and a P picture defined by the MPEG video standard are called core pictures, and the interval between those pictures is called an M value. According to the MPEG video standard, the M value can vary arbitrarily.
In a DVD-Video format stream where the M value varies arbitrarily, the time information calculation on a cell boundary is complex and takes long.
To calculate the time information on a cell boundary, it is necessary to obtain the picture type information in the VOBUs before and after the cell boundary from the video elementary data and to calculate the time information in the DVD-VR format stream that increases monotonously.
Because a V_PCK and an A_PCK can include a plurality of picture frames and audio frames respectively, simply obtaining the V_PTS and V_DTS values from the V_PCK and the A_PTS values from the A_PCK is not enough for calculating the time information. The video and audio elementary data must at least be analyzed at conversion time (for example, coding amount and the number of frames), and the problem is that this requires time for search processing and read processing.
In addition, to extract elementary data from a DVD-Video format stream and to multiplex the extracted data into a DVD-VR format stream, it is necessary to perform calculation considering the limit on the buffers of the DVD-specific video and audio data and then to re-multiplex the video and audio elementary data. This takes a long time.